The invention is directed to a method and to an apparatus for the transport of a band-shaped recording medium having a marginal perforation in an electrographic printer, in particular.
Web-shaped, margin-perforated paper is mainly employed in the electrographic high-performance printer field with printing outputs of more than 40 pages per minute. The recording media are usually made of paper and have lateral holes at their longitudinal edges for transport and for monitoring the position of the paper. It is thereby driven by sprocket tractors that engage into the lateral transport holes. These recording media often also have transverse perforations along which the individual pages are separated from one another, or folds with the aid of which they can be folded together or stacked.
The feed of the perforated paper usually occurs in a specific grid corresponding to the hole spacings. Conventional paper webs have hole spacings of 1/2 inch. The feed can then be accomplished in accordance with 3 steps per hole spacing in a 1/6 inch grid or in accordance with 4 steps per hole spacing in a 1/8 inch grid. The paper web is then not moved continuously but step-by-step by a multiple of the grid spacing.
FIG. 1 shows this type of paper web with a margin perforation. The holes 21 in the margin region of the paper web 5 have a diameter of approx. 1/6 inch and recur at regular intervals of a=1/2 inch. This hole spacing a is the grid width of the hole spacings. When this kind of paper is ready-made for pages whose length can be divided by 1/2 inch, the fold, or respectively, the transverse perforation, that defines the beginning of a page is located precisely in the middle between two margin perforations, as represented by line 22, for example. Given page lengths that can only be divided by 1/6 inch, but not by 1/2 inch, the fold, or respectively, the transverse perforation, can be located on one of the grid lines 23. The fold or transverse perforation is then located in a different place relative to the perforations at the beginning of each page.
FIG. 2 illustrates essential components of printers in accordance with the prior art, which are known under the trademark Oce Pagestream.RTM., for example. A tractor drive 24 is provided in these printers. It comprises a step motor 26, which drives a tractor wheel 25, whose spindles engage in the margin perforations 21 of the paper web 5. The step motor 26 is driven by an electronic control unit 27, which receives clock signals 30 from an image generating unit, on the one hand, and receives clock signals about the current speed of the step motor from a sensor 28, on the other hand. These signals are formed by sampling a timing disk 29 that is connected to the drive shaft of the step motor. The signals of the timing disk correspond to an advance of 1/6 inch; that is, they correspond exactly to the transport grid. The control unit 27 converts the image generation signals 30 in a fixed frequency ratio into drive signals 31 for the step motor 26, which effectuate an advance of 1/6 inch on the paper web, respectively. When the printer is turned on, the drive is initialized. For this purpose, the tractor wheel 25 is aligned to the 1/6 inch transport grid. The control unit 27 generates drive signals in steps of 1/240 inch until it receives a signal from the sensor 28 indicating that a 1/6 inch marker of the timing disk 29 has been detected at the sensor 28.
Once the drive 24 has been aligned to the transport grid, the paper web 5 can be advanced in the 1/6 inch grid such that, with each 1/6 inch step, a reference point, for instance the fold 22, advances exactly from one 1/6 inch increment marker to the next 1/6 inch increment marker on the rule 65 that is fixed to the housing. In the course of initialization, a marker of the paper web 5, for instance the transverse perforation or the fold, is thus positioned at the corresponding page marker (10", 11", 12" or 13") of the rule 65 in 1/6 inch increments. The following pages are then automatically exactly positioned on the basis of the restricted guidance by the sprocket tractor.
Margin perforation is employed particularly in the processing of preprinted paper. In this paper, the information that is to be subsequently added, for instance data that are printed into a preprinted form, should be situated optimally precisely in predetermined locations on the blank.
The perforated paper is usually fed in a defined grid corresponding to the hole spacings, for instance in a 1/2 inch grid or in a 1/6 inch grid. The paper web is moved incrementally by a multiple of the grid spacing.
There is frequently also the demand in the high-performance printing field to be able to employ continuous-form paper that does not comprise such margin perforations in printers for continuous-form paper. Both economic as well as ecological considerations contribute to this demand. Margin-perforated paper is more expensive than paper without margin perforations, since the margin perforations need to be punched in an additional procedure in the course of paper production. An additional processing step is likewise required when printing margin perforated paper for removing the margin strips from the printed page, whereby the waste that thereby arises must be disposed of.
For example, WO 95/19929 A1 discloses a printer that is suitable for processing continuous-form paper without margin perforation which is fed from a roll or stack.
A first seating edge, which prescribes the lateral position of the paper, as well as stabilization rollers, and under-pressure brake and a roller arrangement with a loop-drawing means are provided in this printer for the exact transport of the paper.
Roll papers both with as well as without margin perforation can be fundamentally processed with such a device via a tractorless friction drive. An advantage of this is that paper with margin perforation can still be processed, even though this perforation is not used for transport and guidance of the paper. Papers having margin perforation are frequently still kept in stock in printing centers or are delivered already preprinted. Therefore, it should still be possible to use perforated roll paper in a device which does not necessarily need the margin perforation for transport purposes.
On the other hand, tractorless friction drives have the problem that the transport precision in the feed direction cannot always be adhered to. For example, slippage between the friction roller and the recording medium can contribute thereto.
DE-A-40 39 389 teaches a tractorless drive with which a margin-perforated recording medium can be transported. The transport is controlled by means of a control mechanism, with target positions of the recording medium being computed at reference points and the actual position of the margin holes being detected using a sensor.